The invention relates to the entry feed end of a tenter and the feeding of the fabric selvages to be pinned or clipped to the traveling chains carried by tenter rails. Heretofore, the fabric at the entry end has been placed upon angularly oriented tenter rails which pivot to follow the fabric and convey it on divergent rails which stretch the fabric.
In 90% of the applications, the tenter entry rails pivot either to diverge or converge in accommodating fabric whose width is different than the desired width of the fabric and the tenter. In this case, the selvages of the fabric are pinned onto pins of the tenter chains in a nonparallel condition. This results in scalloping of the fabric at the selvages and skewing of the fabric creating bias lines. The filling yarns are subjected to nonuniform tensions across the fabric creating lines in the fabric.
In other applications of the conventional tenters, the centerline of the fabric is offset from the centerline of the tenter and the tenter entry rails are pivoted parallel to shift the fabric over to the centerline of the tenter. In this situation, the selvages may be pinned or clipped in a more parallel fashion but still at an angle to the entry of the fabric and to the center line of the tenter. This also causes problems in selvage and fabric distortion.
Typical of the above described prior art, are U.S. Pat. Nos. 3,430,301 and 3,147,532.
U.S. Pat. No. 2,673,384 teaches to pin the fabric initially nonparallel and thereafter pass the fabric through parallel sections. However, the initial nonparallel pinning may result in fabric distortion which is continued on throughout the parallel section and onto the main tenter rails.
U.S. Pat. No. 3,150,432 discloses a tenter having pinning rails which may be parallel, but there is little or no positive control of the fabric in the pinning section to ensure straight and accurate pinning. Furthermore, the rails in the pinning section are movable in the direction of fabric travel causing possible stretching during pinning. Tension on the fabric at the pinning area affect accurate control and pinning of the fabric.
U.S. Pat. No. 3,670,375 discloses conventional angular tenter entry rails. A belt is utilized to support and transport the center of the fabric onto tenter rails.
In the prior art overfeed devices, typlified by U.S. Pat. No. 3,147,532, it has been typical to drive overfeed devices at opposing edges of the fabric independently of one another to correct the skew or bias of the fabric. The overfeed drive also serves as a final means to control the per unit weight of the fabric in order to meet the fabric specifications. If it is desired to reduce the weight per square yard of the fabric, then underfeeding is employed. If it is desired to increase the weight of the fabric per square yard in order to meet specifications, then overfeeding may be employed. However, it is desired that the underfeeding or overfeeding be kept within that range only necessary to meet fabric specifications and not to overcompensate. The typical overfeed drive employs a pair of wheels having a nip between which the selvages are fed. Thus, only a point line contact of fabric is had providing little positive control.
In the prior art overdrive systems, the systems have not afforded enough accuracy to control the weight of the fabric as desired. U.S. Pat. Nos. 2,145,044 and 3,604,078 are typical. It has also been known to drive the tenter chains themselves at different speeds in order to correct the skew of the fabric such as in U.S. Pat. Nos. 4,346,621 and 3,839,767.
Another problem in the prior tenter frames has been that of the necessity of having clearance between the ends of the entry rail and the feed roll due to the angular or longitudinal movement of the entry rails. This clearance is needed to allow for the entry rails to pivot either to a divergent or a convergent configuration. To allow the rail to swing in an arc, a sufficient clearance is needed between the end of the rail and the feed roll. However, this angular clearance space creates added distance over which control of the fabric is made difficult and the selvages wander.
Further, due to the temperature differential between ambient temperature and the elevated oven temperatures, considerable thermal expansion of the tenter rails occur resulting in elongation. In order to accommodate the external elongation, it has been necessary to provide additional clearance between the ends of the entry rails and the feed roll. This also increases the uncontrollable space over which the fabric spans and travels from the feed roll to the point of pinning. In this space, the edges of the fabric may tend to wander and lose straightness. The result is that the edges are not pinned on straight to the tenter chains. Numerous devices have been added at the edges of the fabric over this span between the feed roll and pinning point in order to keep the edges straight, requiring additional expense and effort. These devices are commonly referred to as edge uncurlers as shown in U.S. Pat. No. 3,150,432.
The typical overfeed device now found on tenters includes feed rollers which are driven by electric motors. In the normal overfeed or underfeed range of 10%, however, these electric drive motors are susceptible to as much as 50% error in the low speed range. This is because the motors which typically have a 5:1 drive ratio and a 1/2% to 1% speed accuracy over the full range of the motor, results in only a 5% accuracy in the low range of the motor. When it is necessary to underfeed, the electric motor which directly drives the feed roller cannot be driven in a reverse direction, but only slowed down. Thus a true underfeed is not possible but only a drag on the motor is possible due to its freewheeling nature and drag obtained through the friction of the mechanical resistance in the motor gearing. In this case, no accurate control over the rotation of the wheel is actually imparted but rather just resistance to friction slowing the wheel down.
Moreover, in the conventional feed arrangement, a separate electric motor is provided for each side of the overfeed assembly and a separate motor is provided for driving the tenter chain. Upon startup, there is a time lag between the startup of the overfeed motors and the chain drive motor. This can cause creation of a section in the fabric which is either stretched or tremendously overfed compared to the condition of the fabric on the chain. This occurs each time that the fabric is started and stopped. Thus, it can be seen that accurate control of the prior art overfeed systems cannot be had. In particular, no precise control over the underfeeding can be had because no exact control of the negative rotation of the overfeed wheel can be had through direct control of an electric motor.
Moreover, all of the above discrepancies and problems in the prior art require more attention be given to the operation of the tenter requiring increased personnel to be in attendance during operation.
In the prior art overfeed devices, another problem occurs in providing positive control of the fabric. This is, the feed roll of the overfeed drive contacts the fabric at a point of contact and only over a very short distance. This affords only very short gripping and control of the fabric.
Accordingly, an object of the invention is to provide a tenter which may be operated in a more accurate and trouble free manner while accurate control of the weight of the cloth with reduced personnel may be had.
Another object of the invention is to provide a more continuous and positive control over the fabric as it is conveyed or transported through an entry tenter system for pinning.
Another object is to provide apparatus and method for pinning selvages of fabric straight and parallel onto pinning rail sections in a relaxed laid-out state generally without tension, but with positive fabric control.
Another object of the invention is to provide a tenter entry system in which the edges of the fabric are laid on the tenter clips or pins in a straight configuration and a relaxed state so that more even attachment of the fabric occurs in a manner that skew, bias, and other fabric distortions are minimized.
Another object of the invention is to provide a tenter entry feed system wherein more accurate control of the overfeed assembly may be had in order to more accurately control the weight of the fabric produced thorugh the tenter to meet fabric weight specifications.
Another object of the invention is to provide an overfeed drive for the entry end of a tenter wherein underfeed may be controlled in an accurate manner and positive control of the amount of speed subtracted from the overfeed drive may be had.
Yet another object of the invention is to provide an entry feed system for a tenter in which clearance between the main feed roll which feeds the fabric to the entry feed system and the ends of the pinning rails is reduced to a minimum so that control over the fabric is maintained between the feed roll and the point of pinning.
Still another object of the invention is to provide a means for transporting fabric continuously through the pinning rail sections of an entry in a manner that fabric is grasped and conveyed adjacent the feed roll and continued through the pinning point in a positively controlled manner.